She remembers playing on the lawn of her Sussex home, her throat stinging as she swallowed the clouds of crop sprays billowing over the garden hedge.

After several summers, her body began to exhibit symptoms of acute poisoning. When she was 18, it had reached toxic overload. Georgina Downs was admitted to hospital with chronic muscle wastage and neurological damage. Her father, Ray, would soon join her, his eyeballs burnt and his sight forever affected after being caught in a chemical spray while lying on the same lawn. Jeanne, her mother, still suffers acute bouts of fatigue and weakness.

Angered by what she believed had damaged the health of her family, Georgina began asking questions. Her findings proved alarming, suggesting a remarkable failure by ministers to protect the public's health or even to investigate the risks of toxic pesticides sprayed beside people's homes.

Her one-woman campaign not only embarrassed senior Whitehall advisers, but also ultimately put pressure on ministers to acknowledge an issue that may yet lead to a multi-million-pound lawsuit against the government.

This week she will finally learn how successful her crusade has been when the Department for Environment, Food and Rural Affairs (Defra) unveils its response to fresh evidence suggesting a link between the widespread spraying of pesticides and cases of cancer, brain disease and scores of mystery ailments throughout rural Britain. Downs is demanding a 'buffer zone' of at least a mile between crop-sprayed fields and homes, schools and hospitals. More than 25,000 tonnes of pesticides are sprayed every year.

But the Minister of State for sustainable farming and food, Lord Rooker, will this week announce that, instead of introducing mandatory 'buffer zones' around fields, more research on the effect of pesticide sprays is required. Health risks will similarly be played down, amid suggestions from Defra sources that the health concerns over pesticides may be 'all in the mind'. The concern felt by independent experts that Whitehall advisers in charge of pesticide safety are too close to the agrochemical industry will also be rejected.

Downs said: 'To continue not to act and protect communities from pesticides in light of the evidence that exists will put the government in an increasingly untenable position and could have massive legal and political implications. How long must the suffering of rural residents go on? How long can they continue to ignore the scientific evidence? Substantive evidence already exists to demonstrate a serious public health problem.'

Last summer an investigation by the Royal Commission on Environmental Pollution concluded that spraying fields was a potential health risk and could be responsible for diseases including cancer, Parkinson's and ME.

Gaps in the safety data about the risks of pesticides were uncovered. Systems used by officials to quantify health risks were dismissed as 'old science', while the committees designed to assess safety concerns were judged to be too closely connected to the farming industry. Buffer zones of a minimum five metres should be introduced around farms as a precautionary measure, the commission's inquiry recommended. For many, the commission's conclusions were inescapable: the public was not being adequately protected by existing policy.

Downs said: 'Successive governments have continued to deny the evidence. Action needs to be taken to protect the public - not more research, consultations or inquiries'. She is no longer a lone voice. The 33-year-old now presides over a database of more than 900 cases of families whose lives have been blighted by a range of mystery ailments and who all live near fields that are regularly sprayed with pesticides.

On the database is the Cambridgeshire woman who says she convulses before collapsing every time nearby crops are treated, and the West Country woman who recalls clouds of pesticides 'falling like rain' and who is now diagnosed with ME among other debilitating conditions. Other cases include the residents of a hamlet in East Anglia where 12 of the 25 households have reported cases of serious illness linked to the effects of pesticide poisoning.

Ministers have been given warnings about pesticides for more than 50 years. As long ago as 1951, a paper by senior scientists demanded tough powers to limit pesticide use. Even so, Downs discovered that no adequate risk assessment to humans has been carried out, nor have the cumulative effects that chemicals designed to kill organisms might have on humans been sufficiently examined.

Downs also found that farmers, who are advised by manufacturers to wrap themselves in protective clothing, are not legally obliged to inform residents how dangerous the chemical being sprayed near their homes might be, or even what chemical it was.

The official method for assessing the risks to human health is based on the 'bystander' principle, which assumes that people are subject to occasional short-term exposure to chemicals. Tests to analyse the effects of long-term exposure on people living next to a treated field have never been conducted in Britain.

During her campaign, in which she spent thousands of pounds collecting case studies, Downs followed government scientists and harangued them in the hotels where they were staying and publicly challenged government ministers at conferences. She sent letters to pesticide experts, and then challenged their replies.

Last month more evidence supporting a link between exposure to pesticides and ill health surfaced as American scientists claimed that people who were exposed to pesticides were 70 per cent more likely to develop Parkinson's disease: Down's database contains dozens of Parkinson's sufferers.

Last week the EU decided that members states should ensure that residents near cropland should be alerted before farmers begin pesticide spraying. Studies seen by British ministers suggest that pesticide particles have been found up to three miles away from sprayed fields. In the US, seven states require no-spray zones of up to 2.5 miles around schools. A letter from a senior US scientist seen by The Observer argues that buffer zones should be no less than a mile if they are to protect people and animals.

2004 Environment Minister Alun Michael says there is no evidence to support introduction of buffer zones, but requests Royal Commission on Environmental Pollution (RCEP) to carry out an independent study.